In certain types of transportation systems, such as in modern high speed railway and mass and/or rapid transit operations, there is a genuine need for providing an improved wheel-slip detection apparatus which will more safely and efficiently slow down and/or stop the transit vehicles or train at a station or the like. In one given application, it is an authoritative requirement that the wheel-slip controller must be capable of detecting synchronous wheel slip. The definition of synchronous wheel slip is a condition in which all the wheels of the vehicle are slipping at the same or substantially the same deceleration rate. A slip occurs when more braking force is exerted on any one or more wheel axle units than that which can be sustained by the available amount of frictional adhesion that exists between the wheels and the rails. The slipping condition causes the effected axle to decelerate at a higher rate than the vehicle deceleration. In practice, the previous types of wheel-slip control systems reduced the braking force on the slipping axle to a point where it is lower than the equivalent force of the available adhesion. This will stop the axle from decelerating faster than the vehicle and will cause the axle to accelerate back up to the speed of the vehicle. For example, during the time when an axle is decelerating faster than the speed of the vehicle, a velocity differential is developed between the slipping axle and the velocity of the vehicle. In the past, the velocity differential must exceed a predetermined value before any dumping of the brake pressure was initiated. In most cases, the rate of synchronous wheel-slip is less than the rate at which previous wheel-slip controllers take action so that the adverse condition would continue undetected. Thus, it is necessary to produce a condition which will cause the wheel-slip controlling apparatus to initiate corrective measures during synchronous wheel slip for bringing all the axles back to the true velocity of the vehicle.